1. Field of the Invention
This invention relates to a control system for an automatic vehicle transmission, more particularly to a control system for an automatic vehicle transmission, that controls the gear ratio (speed ratio) or driving force so as to reflect the intention of the vehicle operator in the vehicle operation as closely as possible.
2. Description of the Prior Art
As taught by Japanese Patent Laid-Open Application No. Hei 4(1992)-231,218, for example, there are known automatic vehicle transmission control systems or driving force control systems that use two types of driving force control methods.
During uphill driving, these conventional technologies effect control with the desired driving force relative to the throttle valve opening divided in regular increments between the maximum driving force and the minimum driving force so as to enhance the impression of acceleration. During downhill driving, they effect control with the integrated value of past deviation (or error) from the desired vehicle acceleration added to the desired acceleration so as to keep acceleration constant.
Specifically, they calculate the output torque of the engine either from the engine speed, throttle valve opening, amount of intake air etc. or by using a torque converter input-output equation, and then use the so-calculated torque value, a differentiated value (signal ) of the vehicle speed signal and the level running resistance torque to calculate the slope of the road on which the vehicle travels.
However, the conventional technologies do not take into account the slope or other such running conditions and environmental factors. Since they therefore do not reflect driving force change produced by change in running resistance in the case of a slope or the like, they cannot vary the driving force in response to the running state.
Although they are intended to enhance acceleration feel during uphill driving, they cannot produce a specified driving force. Specifically, since they effect control for keeping the desired acceleration constant while correcting for deviation from the desired driving force during past driving, they continue to apply the past correction value even when a change occurs in the slope during downhill driving. The driving force therefore does not necessarily remain constant when the slope changes.
While the prior art control technologies may be able to maintain the acceleration constant, since the control cancels out deviation owing to difference in vehicle weight and the like, it is affected by the past integrated value and therefore cannot keep the integrated value in proper correspondence with the change in slope. This is a cause for unstable control.
Aside from the above, in Japanese Patent Laid-Open Application No. Hei 6(1994)-201,523, it is proposed to estimate the slope of road without using a sensor. In the prior art, specifically, the output torque of the engine is calculated in a similar manner using at least one of the engine speed, the throttle opening and the amount of intake air, etc., and the road slope is estimated based on the calculated output torque, the differentiated value of vehicle speed and the level running resistance such that the gear ratio is controlled based on the estimated road slope.
However, it is difficult in the prior art to estimate the road slope accurately, while avoiding the lag of estimation. As a result, the prior art is disadvantageous in that it would not be able to attain the expected result when conducting the gear ratio control using the estimated road slope.
This invention is directed to overcoming the foregoing drawbacks. One object of the invention is to provide a control system for an automatic vehicle transmission that, focusing on the fact that the quality of drivability varies markedly during hill climbing and descent, estimates the slope, discriminates climbing, descending and other driving states, and controls the gear ratio (speed ratio) in response to the discrimination so as to achieve the desired driving force and enhance drivability.
Another object of the invention is to provide a control system for an automatic vehicle transmission that calculates an evaluation indicator signifying drivability tendency and controls the gear ratio (speed ratio) in response to the calculated evaluation indicator, thereby enhancing drivability.
Still another object of the invention is to provide a control system for an automatic vehicle transmission that estimates the road slope accurately, without estimation lag, and controls the gear ratio (speed ratio) optimally, thereby enhancing drivability.
In order to achieves these objects, according to the first aspect of this invention, there is provided a system for controlling an automatic transmission of a vehicle having an input shaft connected to an internal combustion engine mounted on the vehicle and an output shaft connected to driven wheels of the vehicle, the transmission transmitting output torque generated by the engine and inputted through the input shaft to the driven wheels through the output shaft, wherein the improvement comprises: operating condition detecting means for detecting operating conditions of the engine and the vehicle including at least a vehicle speed and a throttle opening; running resistance calculating means for calculating a running resistance acting on the vehicle;driving force calculating means for calculating a driving force generated by the vehicle; slope estimating means for estimating a slope of a road on which the vehicle travels based on at least the calculated running resistance and the driving force; running state discriminating means for comparing the estimated slope with a predetermined value and for discriminating a running state of the vehicle; gear ratio determining means for calculating a maximum driving force to be generated by the vehicle at a current gear ratio to calculate a driving force difference from the calculated driving force and for determining a gear ratio such that the driving force difference is a predetermined value in response to the discriminated running state; and transmission operating means for operating the transmission in response to the determined gear ratio.
In order to achieves these objects, according to the second aspect of this invention, there is provided a system for controlling an automatic transmission of a vehicle having an input shaft connected to an internal combustion engine mounted on the vehicle and an output shaft connected to driven wheels of the vehicle, the transmission transmitting output torque generated by the engine and inputted through the input shaft to the driven wheels through the output shaft, wherein the improvement comprises:operating condition detecting means for detecting operating conditions of the engine and the vehicle including at least a vehicle speed and a throttle opening; actual driving force calculating means for calculating an actual driving force generated by the vehicle based on at least the detected throttle opening; operator desired estimating means for estimating an operator desire estimated value desired by a vehicle operator based on at least the detected throttle opening; indicator conversion means for converting the actual driving force and the operator desire estimated value to an evaluation indictor; running characteristic discriminating means for discriminating based on the evaluation indicator which of a first running characteristic and a second running characteristic, which are different in driving force response, the vehicle operator wants; and driving force controlling means for controlling a driving force of the vehicle through at least one of an output of the engine and a gear ratio in accordance with the discriminated running characteristic.